Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$12.50	6.274%	$13.2843	$13.28	$13.30	$13.30
Purchase #2	$47.31	13.199%	$53.5544	$53.55	$53.55	$53.60
Purchase #3	$48.30	9.574%	$52.9242	$52.92	$52.90	$52.90
Purchase #4	$86.43	8.558%	$93.8267	$93.83	$93.85	$93.80
Purchase #5	$136.71	7.227%	$146.59	$146.59	$146.60	$146.60
Purchase #6	$91.71	6.326%	$97.5116	$97.51	$97.50	$97.50
Purchase #7	$122.65	5.102%	$128.9076	$128.91	$128.90	$128.90
7 purchase totals =	$545.61		$586.5988	$586.59	$586.60	$586.60